Structural characterization suggests models for monomeric and dimeric forms of full-length ezrin

Ezrin is a member of the ERM (ezrin–radixin–moesin) family of proteins that have been conserved through metazoan evolution. These proteins have dormant and active forms, where the latter links the actin cytoskeleton to membranes. ERM proteins have three domains: an N-terminal FERM [band Four-point-one (4.1) ERM] domain comprising three subdomains (F1, F2, and F3); a helical domain; and a C-terminal actin-binding domain. In the dormant form, FERM and C-terminal domains form a stable complex. We have determined crystal structures of the active FERM domain and the dormant FERM:C-terminal domain complex of human ezrin. We observe a bistable array of phenylalanine residues in the core of subdomain F3 that is mobile in the active form and locked in the dormant form. As subdomain F3 is pivotal in binding membrane proteins and phospholipids, these transitions may facilitate activation and signaling. Full-length ezrin forms stable monomers and dimers. We used small-angle X-ray scattering to determine the solution structures of these species. As expected, the monomer shows a globular domain with a protruding helical coiled coil. The dimer shows an elongated dumbbell structure that is twice as long as the monomer. By aligning ERM sequences spanning metazoan evolution, we show that the central helical region is conserved, preserving the heptad repeat. Using this, we have built a dimer model where each monomer forms half of an elongated antiparallel coiled coil with domain-swapped FERM:C-terminal domain complexes at each end. The model suggests that ERM dimers may bind to actin in a parallel fashion

The photophysics of cryptophyte light-harvesting

Recent studies of the optical properties and the critical role of phycobiliproteins in the absorption of green light for photosynthesis in cryptophyte algae (Rhodomonas CS24 and Chroomonas CCMP270) are reviewed. Investigations of two different isolated proteins, phycoerythrin 545 (PE545) and phycocyanin 645 (PC645), whose crystal structures are known to 0.97 and 1.4 Å resolution respectively, are described. Steady-state spectroscopic measurements, including polarization anisotropy and circular dichroism, are used in combination with ultrafast transient grating and transient absorption techniques to elucidate a detailed picture of resonance energy transfer within the light-harvesting proteins. Quantum chemical calculations are employed to estimate phycobilin excited states, and generate transition density cubes which are used to calculate accurately the electronic coupling between the chromophores in PE545 and PC645. Energy transfer dynamics are examined using the generalized Förster theory. Kinetic models for energy transfer dynamics in both proteins are presented for comparison. Investigations of energy transfer from phycoerythrin 545 to chlorophyll-containing light harvesting complexes and photosystems in the intact algae Rhodomonas CS24 and Chroomonas CCMP270 are also reported. © 2006 Elsevier B.V. All rights reserved

Crystal Structure of A 1.70 A Archaeal Sm Protein Complex

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Going it Alone: Homomeric Ring Assemblies of Eukaryotic SM Proteins

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Ringing RNA: Homomeric Assembly of Yeast SMF Protein

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Ringing RNA: SM protein stacks from archaea to yeast

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Glimpsing the evolution of the spliceosome: crystal structure of an Archaeal Sm protein

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Time-dependent motor properties of multipedal molecular spiders

Molecular spiders are synthetic biomolecular walkers that use the asymmetry resulting from cleavage of their tracks to bias the direction of their stepping motion. Using Monte Carlo simulations that implement the Gillespie algorithm, we investigate the dependence of the biased motion of molecular spiders, along with binding time and processivity, on tunable experimental parameters, such as number of legs, span between the legs, and unbinding rate of a leg from a substrate site. We find that an increase in the number of legs increases the spiders' processivity and binding time but not their mean velocity. However, we can increase the mean velocity of spiders with simultaneous tuning of the span and the unbinding rate of a spider leg from a substrate site. To study the efficiency of molecular spiders, we introduce a time-dependent expression for the thermodynamic efficiency of a molecular motor, allowing us to account for the behavior of spider populations as a function of time. Based on this definition, we find that spiders exhibit transient motor function over time scales of many hours and have a maximum efficiency on the order of 1%, weak compared to other types of molecular motors